Temperature measuring resistance

ABSTRACT

A temperature measuring resistance employing a composition whose electrical resistance varies with temperature. The composition is preferably a glass containing Al2O3, LiO2 and SiO2.

United States Patent [191' Kristen Jan. 15, 1974 TEMPERATURE MEASURING RESISTANCE [75 Inventor: Klaus Kristen, Wiesbaden, Germany References Cited [73] Assignee: Jenaer, Glaswerk, Schott, and Gen., UNITED STATES PATENTS Wiesbaden, Germany 3,162,831 12/1964 Heath 338/21 3,216,808 H 1965 B h l. 106 47 R X [22 Filed: Aug. 8, 1972 eta [2]] Appl. No.2 278,828 Primary ExaminerC. L. Albritton Attorney-David R. Murphy et al. [30] Foreign Application Priority Data Aug. 9, 1971 Germany P 21 39 828.7 [57] ABSTRACT A temperature measuring resistance employing a com- U-S. Cl. R, position h se electrical resistance aries tem- Int. peraturep The composition is preferably a glass Con. [58] Field of Search 338/20, 21, 13, 22, mi i A1 0 LiO and S10 7 Claims, 4 Drawing Figures PAYENTEUJWS 1974 3 786 390 sun-:1 2 OF 2 TEMPERATURE MEASURING RESISTANCE The invention relates to a temperature-measuring resistance.

Temperature-measuring resistances having a negative temperature coefficient are already known. These are thermistors having negative temperature coefficients and consisting of n-conducting semiconductor materials. Their resistance decreases by 2.5 to 4.5 percent per degree centigrade.

The conditions which are set as regards the stability and capacity for reproduction of the resistance characteristics of the NTC resistances are only satisfied by certain metal oxides or oxidic mixed crystals with a common oxygen lattice. There are, for example:

a. mixed crystals of Fe O. (spinel) with substances which likewise present spinel lattice structures, as for example Zn TiO and MgCr O b. Fe O with additions of TiO c. MO or C and also combinations of these oxides with small additions of Li O.

The dependence on temperature of the NTC resistance is represented as an approximation by the equation:

RT: A 817 In which R, represents the resistance of the thermistor at the temperature T, measured in l(.

A represents a constant with the dimension of ohms and dependent on the form of construktion of the resistance.

B represents a constant which depends on the form of construktion and the material of the thermistor with the dimension K.

e represents the base of the natural logarithms The following applies regarding the temperature coefficient of the NTC resistances:

Typical B-values lie between 2 X 10 and 6 X 10 K.

NTC resistances are produced by pressing the initial compositions obtained from the aforementioned materials and subsequent sintering at high temperatures.

Depending on the form of construction, the temperature range in which they can be used varies between 25C and a maximum of 350C.

This relatively low maximum temperature of use is a serious disadvantage of the known NTC resistances.

The present invention has for its object a temperature-measuring resistance which does not present these disadvantages of the known NTC resistances, has the same or larger temperature coefficients, but is capable of being used in substantially higher temperature ranges, for example up to 700C.

According to the present invention, there is provided a temperature-measuring resistant having two contacts and having therebetween a composition whose electrical resistances varies with temperature. The composition comprises broadly the following compounds in the following percentages by weight:

Compound Weight Percent Al,0, 14 to 32 Li,O 1 to 6 SiO, balance and preferably comprises:

Al,0, 14 to 32 up to 6 Tio 0.5 to e Zro 0.5 to 5 SiO, balance In this way, there is utilized the specific resistance of glass or of glass ceramics, which is strongly variable with the temperature. What has been found to be particularly advantageous is the small linear expansion coefficient of the glass ceramics, which is in the order of magnitude ofO to 30 X 1O"' and permits unrestricted use of the temperature-measuring resistances with quickly changing temperatures and large differences in temperature. The maximum temperatures of use are thus substantially higher than those of the known NTC resistance.

According to the invention, the resistance material consists of a glass ceramic with large negative temperature coefficients and has heat-expansion coefficients less than 30 10 By contrast with the NTC resistances of which the conductivity depends on the electron conduction, the conductivity of the glass ceramics is caused purely by ion conduction. The conductivity thus depends primarily on the concentration and the mobility of the alkali ions in the glass ceramic. Hence, the conduction process is very complex and ifinfluenced by the nature and composition of the crysal phase and the glass phase, also by the absolute quantities of the glass phase and crystal phase and also by the structural formation. Consequently, suitable as thermistors are particularly al kali-containing glass ceramics, more especially glass ceramics of SiO -Al O Li O, since these have, in addition to the necessary conductivity, a good resistivity to change in temperature because of their low heatexpansion coefficient of 0 to 15 X 10". Such glass ceramics are described in the German Offenlegungsschrifts 1,596,855 and 1,596,860, and also in German Patent Specification 1,596,858.

In the same way as with glasses, the curve of the specific resistance with the temperature in connection with glass ceramics for temperatures below the transformation range, is described by the law of Rasch and Minrichsen:

log.p A (B/T),

which, with a renomination of the constants, can also be written in the form:

p1 blT with which the main conformity of the resistance curve with that of the NTC resistances becomes clearly apparent.

As with glasses, the value of the constant B lies between 3 X 10 and 6 X 10 K. The value A varies between +1.5 and 4.5.

Using the Rasch-Hinrichschen law, and by differentiation of the temperature coefficients, there is obtained:

A glass ceramic of the aforementioned system Si- O -Al O -Li O has for example a B-value of 4.75 10 K.

Thus, at 573K, there is obtained a temperature coefficient of 3.3 percent per degree centigrade.

Glass ceramic thermistors can only be operated with alternating current. When using direct current, the ions which participate in the conduction are depleted and in a short time the resistance is strongly increased.

Depending on the shape which is required, thermistors of glass ceramics are shaped by known glassprocessing procedures such as pressing, rolling and blowing and can be transformed into a polycrystalline material in a second processing step by a controlled heat treatment.

The temperature range in which the glass ceramic thermistors can be used has an upper limit, which is the temperatureat which the permanent deformations, for example, due to a continuation of the crystallization, are produced. The lower limit as regards the range of use is only given by the maximum resistance which can still be accepted for the respective purpose of use.

In the Drawings FIG. I shows in the form ofa graph the typical curve of the resistance, depending on the temperature for the temperature-measuring resistance according to the invention.

FIGS. 2 and 3 show two constructional examples of temperature-measuring resistances according to the invention.

FIG. 4 shows an embodiment of the temperature measuring resistances in the form of a pressed glass melt.

The temperature-measuring resistance shown in FIG. 2 can for example be produced by a platinum wire loop being placed between two glass ceramic wafers which have still not assumed ceramic form and this sandwich is then melted under pressure at high temperature and simultaneously converted into the polycrystalline state. After terminating the temperature treatment, the platinum wire loop is severed and the temperaturemeasuring element is brought to its final shape by grinding and polishing.

FIG. 3 shows a glass ceramic article, namely, a glass ceramic plate, which has a zone 1 formed as a temperature-measuring resistance. This zone 1 is produced by two conductive silver strips 2 being fired on the said plate. When the plate is heated, the zone as thus defined can serve as temperature detector for controlling the plate temperature. As compared with the use of a thermoelernent, it has proved to be advantageous that the mean temperature of a surface and not just the temperature of a point is determined.

FIG. 4 shows an embodiment of the temperaturemeasuring resistances in the form of a pressed glass melt. The glass 1 is located between an outer electrode 2 in the form ofa ring and an inner electrode 3 ofa suitable metal.

In order to minimize the adverse effects of rapid temperature changes, the use of glass as a resistance material is possible. The relation of specific electrical resistance to temperature is quantitative in the case of glasses as in the case of glass ceramics. Among the advantages of the use of glass as a resistance material is the ability to use mixtures of glasses whose resistance gradient can be made to vary over wide ranges. Above all, it is possible to provide given resistance values for given temperatures.

Temperature-measuring resistances having an outstanding temperature expansion coefficient can be provided in different physical forms. For example, the

temperature-measuring element can be provided in the form of a pressure glass melt or as an element having a very small mass.

The invention may be better understood by reference to the following specific example employing a specific glass composition.

Example A temperature-measuring resistance is fashioned as shown in FIG. 2 employing as the wafers the glass ceramic shown in Column 1 of Table I beginning at Line 27, Column 5 of Auslegeschrift 1,596,858. The resultant temperature-measuring resistance functions satisfactorily.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

What is claimed is:

l. A temperature-measuring resistance having two contacts and having therebetween a composition whose electrical resistance varies with temperature, said composition comprising the following compounds in the following percentages by weight:

Compound Weight Percent AI O l4 to 32 Li O l to 6 SiO balance 2. The resistance of claim 1 wherein the compoisition comprises the following compounds in the following percentages by weight;

Compound Weight Percent A1 0 14 to 32 U 0 1 to 6 TiO 0.5 to 6 ZrO, 0.5 to 5 SiO, balance 3. A temperature-measuring resistance according to claim 1, characterized in that the composition consists ofa glass ceramic with a high negative temperature coefficient.

4. A temperature-measuring resistance according to claim 1 characterized in that the glass ceramic of the resistance material has a thermal expansion coefficient smaller than 30 X lO' /C.

5. A temperature-measuring resistance according to claim 1 characterized in that a glass ceramic article shows certain measuring ranges due to defining contacts.

6. A method of measuring temperature by passing a current through a composition whose electrical resistance varies with temperature, said composition comprising the following compounds in the following percentages by weight:

Compound Weight Percent A1 0 14 to 32 U 0 1 to 6 SiO balance 7. The method of claim 6 wherein the composition comprises the following compounds in the following percentages by weight:

Compound Weight Percent A1 0 14 to 32 U 0 1 to 6 TiO 0.5 to 6 ZrO 0.5 to 5 SiO balance. 

2. The resistance of claim 1 wherein the composition comprises the following compounds in the following percentages by weight: Compound Weight Percent Al2O3 14 to 32 Li2O 1 to 6 TiO2 0.5 to 6 ZrO2 0.5 to 5 SiO2 balance
 3. A temperature-measuring resistance according to claim 1, characterized in that the composition consists of a glass ceramic with a high negative temperature coefficient.
 4. A temperature-measuring resistance according to claim 1 characterized in that the glass ceramic of the resistance material has a thermal expansion coefficient smaller than 30 X 10 7/*C.
 5. A temperature-measuring resistance according to claim 1 characterized in that a glass ceramic article shows certain measuring ranges due to defining contacts.
 6. A method of measuring temperature by passing a current through a composition whose electrical resistance varies with temperature, said composition comprising the following compounds in the following percentages by weight: Compound Weight Percent Al2O3 14 to 32 Li2O 1 to 6 SiO2 balance
 7. The method of claim 6 wherein the composition comprises the following compounds in the following percentages by weight: Compound Weight Percent Al2O3 14 to 32 Li2O 1 to 6 TiO2 0.5 to 6 ZrO2 0.5 to 5 SiO2 balance. 